Tissue engineering is generally defined as the creation of tissue or organ equivalents by seeding of cells onto or into a scaffold suitable for implantation. The scaffolds must be biocompatible and cells must be able to attach and proliferate on the scaffolds in order for them to form tissue or organ equivalents. These scaffolds may therefore be considered as substrates for cell growth either in vitro or in vivo.
The attributes of an ideal biocompatible scaffold would include the ability to support cell growth either in vitro or in vivo, the ability to support the growth of a wide variety of cell types or lineages, the ability to be endowed with varying degrees of flexibility or rigidity required, the ability to have varying degrees of biodegradability, the ability to be introduced into the intended site in vivo without provoking secondary damage, and the ability to serve as a vehicle or reservoir for delivery of drugs or bioactive substances to the desired site of action.
A number of different scaffold materials have been utilized, for guided tissue regeneration and/or as biocompatible surfaces. Biodegradable polymeric materials are preferred in many cases since the scaffold degrades over time and eventually the cell-scaffold structure is replaced entirely by the cells. Among the many candidates that may serve as useful scaffolds claimed to support tissue growth or regeneration, are included gels, foams, sheets, and numerous porous particulate structures of different forms and shapes.
Among the manifold natural polymers which have been disclosed to be useful for tissue engineering or culture, one can enumerate various constituents of the extracellular matrix including fibronectin, various types of collagen, and laminin, as well as keratin, fibrin and fibrinogen, hyaluronic acid, heparin sulfate, chondroitin sulfate and others.
Other common polymers that were used include poly(lactide-co-glycolide) (PLG). PLG are hydrolytically degradable polymers that are FDA approved for use in the body and mechanically strong (Thomson R C, Yaszemski M J, Powers J M, Mikos A G. Fabrication of biodegradable polymer scaffolds to engineer trabecular bone. J Biomater Sci Polym Ed. 1995; 7(1):23-38; Wong W H. Mooney D J. Synthesis and properties of biodegradable polymers used as synthetic matrices for tissue engineering. In: Atala A, Mooney D J, editors; Langer R, Vacanti J P, associate editors. Synthetic biodegradable polymer scaffolds. Boston: Birkhäuser: 1997. p. 51-82). However, they are hydrophobic and typically processed under relatively severe conditions, which make factor incorporation and entrapment of viable cells potentially a challenge.
As an alternative, a variety of hydrogels, a class of highly hydrated polymer materials (water content higher than 30% by weight), have been used as scaffold materials. They are composed of hydrophilic polymer chains, which are either synthetic or natural in origin. The structural integrity of hydrogels depends on cross-links formed between polymer chains via various chemical bonds and physical interactions.
For example, document U.S. Pat. No. 6,586,246 B1 has disclosed a method for preparing a porous hydrogel scaffold which may be used as supports for tissue engineering or culture matrices. The method of the document comprises the steps consisting of a) dissolving a biodegradable synthetic polymer in an organic solvent to prepare a polymeric solution of high viscosity b) adding a porogen agent to this solution; c) casting the polymer into a mould d) removing the organic solvent e) submerging the organic solvent-free polymer/salt gel slurry in a hot aqueous solution or acidic solution to cause the salt to effervesce at room temperature to form the porous scaffold. However, this method of preparation of a porous hydrogel involves the use of an organic solvent with a synthetic polymer which renders the method according to this invention weakly compatible with biological and therapeutic purposes.
Therefore there is still an existing need in the art to develop a method for preparing porous scaffold matrices that can be used for biological and therapeutic purposes.